Many buildings may have a doorway with a loading dock to facilitate transferring cargo between a truck and the building. A loading dock is a platform that is generally at the same elevation as the bed of the truck or its trailer. The dock may also include a dock leveler, which is a vertically movable ramp that compensates for a height differential that may exist between the platform and the truck bed. Dock levelers may also provide a bridge across which personnel and material handling equipment can travel between the platform and the truck.
For protection against weather and theft, the doorway of the building may include a manual or power operated door. Doors for loading docks usually open and close by moving vertically so as not to interfere with the rear of the truck or interfere with cargo and activity just inside the doorway; however, other types of doors can be used.
When there is no truck at the dock and the weather is mild, the door may be left open to help ventilate the building with fresh outside air. Leaving the door open, unfortunately, increases the risk of personnel or material handling or other equipment inside the building from accidentally falling off the edge of the dock's platform and through the open doorway to the driveway. In addition, the door being left open decreases building security due to entrance of unauthorized personnel or employee theft via the unsecured doorway.
To provide ventilation through the doorway while minimizing the falling hazard, some loading docks include a runoff barrier that provides an obstruction across the doorway when a truck is not present or otherwise moves to a nonblocking position as needed. Examples of such barriers are described in U.S. Pat. Nos. 5,271,183 and 5,299,386.
Regardless of whether a loading dock includes a runoff barrier, a forklift transferring cargo between the truck's trailer and the dock's platform can present a collision hazard for dockworkers or other people in the work area. If a forklift is operating deep inside the truck's trailer, the forklift driver and nearby pedestrians might not notice each other. Thus, the forklift might suddenly emerge from within the trailer and accidentally strike someone.